1. Field of Invention
This invention relates to all applications where there is a requirement in which reflectivity of incident light (visible through infrared) in one direction and transmissivity in the opposite direction are simultaneously enhanced. That is, the sum of the reflectivity from one side and the transmissivity from the other side exceeds 1.0. Such a film will hereinafter be called a multiflector.
One application area is for solar collection in which transmission of light would be maximized (reflectivity minimized) in the direction facing the sun and reflectivity maximized (transmissivity minimized) in the direction facing the collector. The invention will significantly increase the level of retained energy in such devices. Additionally, the invention could be used as part of a heating, cooling and/or power generating system in which solar energy is utilized for some or all of the power generation. The invention will increase the efficiency of solar collectors and will thus reduce the use of fossil fuels.
A second application area includes use with any non-emissive display technologyxe2x80x94such as electrochromic, ferroelectric, ferromagnetic, electromagnetic, and liquid crystalxe2x80x94where it is desired to use both externally generated (ambient) light and internally generated (artificial) light. The film is a replacement for the transflective/reflective/transmissive element of the non-emissive displays, where the replaced element is either independent of or integral to the internally generated light (backlight system). Use of this film will allow brightness contributions simultaneously from artificial light and ambient light such that systems will see a significant decrease in power usage. In system where a battery is used for some or all of the power supply, battery life can be increased by as much as 174%.
A third application area includes building materials in which a film can be used to direct light from a light source (such as a window or skylight) while at the same time reflecting ambient light within a building or structure.
2. Description of Prior Art
Solar Collectors
The prior art for solar collectors includes photovoltaics where sunlight is converted directly to electricity, solar thermal energy used to heat water, and large scale solar thermal power plants used to generate electricity. In these systems solar energy is xe2x80x9ccollectedxe2x80x9d by placing panels or arrays of panels in the direct path of the sun. These panels are composed of mirrors or mirror-like material to reflect solar energy to a specific point for collection, or are made up of a variety of absorbent materials. Systems where absorbent materials are used can be further be divided into systems where solar energy is collected in cells or where solar energy is absorbed as thermal energy to heat either water or a heat-transfer fluid, such as a water-glycol antifreeze mixture. Most commercially available solar cells are made from wafers of very pure monocrystalline or polycrystalline silicon. Such solar cells, typically, can attain efficiencies of up to 18% in commercial manufacture. The silicon wafers used to make them are relatively expensive, making up 20-40% of the final module cost. The alternative to these xe2x80x9cbulk siliconxe2x80x9d technologies is to deposit a thin layer of semiconductor onto a supporting material such as glass. Various materials can be used such as cadmium telluride, copper-indium-diselenide and silicon. There are basically three types of thermal collectors: flat-plate, evacuated-tube, and concentrating. A flat-plate collector, the most common type, is an insulated, weatherproofed box containing a dark absorber plate under one or more transparent or translucent covers. Evacuated-tube collectors are made up of rows of parallel, transparent glass tubes. Each tube consists of a glass outer tube and an inner tube, or absorber, covered with a selective coating that absorbs solar energy well but inhibits radiative heat loss. The air is withdrawn (xe2x80x9cevacuatedxe2x80x9d) from the space between the tubes to form a vacuum, which eliminates conductive and convective heat loss. Concentrating collector applications are usually parabolic troughs that use mirrored surfaces to concentrate the sun""s energy on an absorber tube (called a receiver) containing a heat-transfer fluid.
Emissive Displays
The prior art for non-emissive displays, particularly liquid crystal displays, include either reflective displays or surface light source (transmissive) displays, commonly denoted backlit displays. The conventional reflective display which uses a reflective film as the bottom layer to redirect ambient light back through the display elements has a composition as illustrated in FIG. 1. In this drawing ambient light 10 (sunlight, artificial lightxe2x80x94such as office lightingxe2x80x94or from a light source 11 attached to the top of the unit) enters the display unit, passes through the various layers of the unit, 6 polarizers, 7 glass plates (which may include color filters, common electrodes, TFT matrix, or other components), and 8 liquid crystal suspension, and is redirected from the reflective film 9 back through the various layers to produce an image. This method of creating an image with available ambient light is limited by the available light. This method is not an effective means for producing high quality graphic images and severely limits the quality of color images in a variety of conditions. The conventional backlit (transmissive) display has a composition as illustrated in FIG. 2. In this drawing, light is produced with a backlight assembly 7 and directed as light ray 13, through the various layers, such as 6 polarizers, 7 glass plates (which may include color filters, common electrodes, TFT matrix, or other components), and 8 liquid crystal suspension, to produce an image. This method of producing an image with artificial light is limited by the amount of ambient light and, in systems where a battery is used some or all of the time to generate power, by limited battery life. When ambient light is present, glare is created by light reflecting off the various layers, as described above, without passing through all the layers 6 through 8. To overcome this glare and to produce an image that is palatable to a user, the backlight gain must be increased to produce more usable light, i.e. more light passing through layers 6 through 8. This increase in artificial light causes an added drain on the battery and thus reduces the usability of the system to which the display is attached. As ambient light increases, glare increases and thus, at some point the backlight becomes ineffective in producing a palatable image.
Previous attempts to use simultaneously the ambient light and a backlight have resulted in applications that compromise both the transmissive qualities and the reflective qualities of the display. Hochstrate, in U.S. Pat. No. 4,196,973 teaches the use of a transflector for this purpose. Weber, in U.S. Pat. No. 5,686,979, col. 2, teaches the limitations of the transflector for this purpose and alternatively proposes a switchable window that at one time is wholly transmissive and at another time is wholly reflective.
Building Materials
The prior art for building materials is related to films or coatings for light sources (such as windows, skylights, or light pipes) in which the control of transmittance and/or reflection of light is desired. Films or coatings generally fall within two categories: tinting or reflecting materials. Tinting materials have the quality of reflecting a certain percentage of light from one side of the film while transmitting the remainder of the light. In tinting films or coatings, the ratio of transmittance/reflectance is determined by the properties of the material(s), and is the same on either side of the film (Reflectivity R+Transmissivity T=1). For reflective films or coatings, the reflectivity R is less than or equal to 1, where the limit is determined by the properties of the material.
Objects and Advantages
A primary object of this invention is to direct light in such a manner as to reflect incoming light from one direction with minimal loss of said light and with controlled redirection of said light, while at the same time transmitting light from the opposite direction with minimal loss of said light and with minimal redirection of said light.
Another object of this invention is to direct light in such a manner as to transmit incoming light from one direction with minimal loss of said light and with minimal redirection of said light, while at the same time reflect light from the opposite direction with minimal loss of said light and with controlled redirection of said light in such a manner as to contain said light within a system, i.e. solar collector, or structure (such as an office building, museum, etc.).
The Multiflecting Light Directing Film according to the present invention will increase the brightness and reduce the effects of glare in systems where this is required and/or will increase the efficiency of systems where containing light is required.